Apparatus for measuring thickness of sheet material



Jan. 5, 1954 2,665,333

APPARATUS RoR MEASURING THTCKNRSS oF SHEET MATERIAL D. w. DuNlPAcE ET AL3 Sheets-Sheet l Filed NOV. 30, 1950 @@cvza Kde@ Jan. 5, 1954 D. w.DUNIPACE ETAL 2,665,333

APPARATUS FOR MEASURING THICKNESS OF SHEET MATERIAL Filed Nov. so, 195o3 Sheets-Sheet 2 nnentor Bg .amd @Mmm @wwe Gttorneg Jan. 5, 1954 D. w.DUNIPACE ETAL 2,665,333

APPARATUS FOR MEASURING THICKNESS OF SHEET MATERIAL Filed Nov. 30, 19505 Sheets-Sheet 3 Zsnventorg Gttornegg Patented Jan. 5, 1954 APPARATUSFOR MEASURING THICKNESS F SHEET MATERIAL Donald W. Dunipace and NormanC.

Nitschke,

Perrysburg, Ohio, assignors to Libbey-Owens- Ford Glass Company, Toledo,Ohio, a corporation of Ohio Application November 30, 1950, Serial No.198,412

Claims.

The present invention relates broadly to mprovements in inspectionapparatus.

More particularly, the invention has to do with a novel gaging apparatusto continuously inspect and record the thickness or variation inthickness of sheet material which can only be contacted on one of itssurfaces.

Heretofore, it has been customary practice in the nishing of sheetmaterial, such as for eX- ain'ple plate glass, to periodically removespecimen samples from various areas and inspect the same by means ofconventional thickness measuring instruments. This is perhaps but one ofseveral practices attempted in an endeavor to afford a periodic check ofthe sheet material while still in a partially iinished condition.Obviously, when a. selected sample has been examined, the remainder ofthe sheet from Which the sample Was taken may have passed beyond anypoint at which its finishing could have been varied in one way oranother to better its quality, or control the thickness thereof. Thisexample and like methods of inspection have been employed during thegrinding and polishing of plate glass and While the sheets are securedin plaster upon the tops of a line of Work tables moving continuouslybeneath ya series of grinding and polishing elements. Those acquaintedwith this phase of plate glass manufacture will readily appreciate thedifficulties heretofore experienced in attempting to obtain the glassthickness since only the upper surface thereof is exposed to eX-amination, the bottom surface being embedded in a layer of plaster ofParis or the like which secures the sheet in its entirety to the uppersurface or deck of the work table.

Various practical objections have entered into Vthe possible solution ofthis problem, since any surface contacting the glass is susceptible toWear, mechanical friction and/or vibration either or" the tables or fromthe grinding and polishing elements. Now, however, it has beendiscovered that by the use of a novel free hydraulic support, a gagingdevice may be disposed in such physical contact to the surface of aglass sheet that the thickness thereof can be accurately determined tovery close dimension and an effective continual control exerted by theoperator, enabling him either to make immediate adjustments in thegrinding and polishing operations or tc follow definite areas of glasson the grinding tables to the completion of their polishing.

It is therefore an aim of this invention .to provide Yan improvedinspection apparatus foriaccurately measuring, and recording if desired,the thickness of a glass sheet while it is secured to a supportingsurface and moving therewith so that only its upper surface can becontacted.

Another object of the invention is to provide an inspection apparatus ofthe above character which embodies magnetically operated means mountedabove a moving sheet of glass at a predeterminable distance therefrom inorder that a magnetic field can be created with reference to the top ofthe work table on which the glass is carried.

Another object of the invention is to provide an inspection apparatus ofthe above character which includes a magnetic instrumentality and asupporting case therefor, said supporting case being carried in ridingcontact with the surface of va glass sheet by an interposed fluid lm ofpredetermined thickness whereby the magnetic instrumentality will besupported above the top of a grinding table and the character of themagnetic eld created therebetween be made rapidly responsive accordingto the thickness of the glass sheet then passing beneath said case.

A further object of the invention is to provide in an inspectionapparatus of the above character, a magnetic device including asupporting case therefor, and means for hydraulically supporting thecase upon the surface of a glass sheet, said case and magnetic devicebeing adjustably movable with respect to one another to permit primarylocation of said magnetic device in vertical relation to the under faceof the case according to the prescribed thickness of glass sheets to beinspected.

A further object of the invention is to provide in an inspectionapparatus of the above character, a magnetic instrumentality whichembodies magnetically operated means mounted above 'a moving sheet ofglass at a predeterminable distance and a magnetic reference platedisposed at a predeterminable distance beneath said moving sheet ofglass whereby a magnetic eld can be created with reference to the top ofthe said reference plate and the character of said magnetic field bemade rapidly responsive to the thickness of the glass sheet then passingthrough said magnetic field.

A further object of the invention is to provide in an inspectionapparatus of the above character, a magnetic device including asupporting case therefor, and means for hydraulically supporting thecase upon the surface of a glass sheet, in combination With a magneticplate dis- A still further object of r`the.-inventiornisl` toVVV providea gaging head and a magnetic device carried therein, and means forsupporting the gaging head by means of a liquid lrn on a moving sheet ofglass, in combination withga recording and indicating system whereby themagnetic device will produce electrical responses within said system torecord and/or continuously indicate the thickness of the moving sheet ofglass` A still further object or,Y the invention is to provide a gaginghead and a magneticv device carriedvtherein and a referenceplate adaptedto complete a magnetic eld created by IsaiddeiIice, means for supportingthegaging head and the reference plate byrrneans of iiuid nlms in spacedrelation to a moving sheetof glass in combination with ka recording andvindicating system whereby the magnetic device will produce electricalresponses within said system to record and/ or continuously lindicatethe thickness ol the moving sheetof glass.

Other objects and advantages of the invention will .become more-apparent during the course of the Yfollowing description when taken inconnection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate, likepartsy throughout the same:

Fig. l is a perspective view'of inspection apparatus constructed inVaccordance :with the invention and mounted upon a sheet of glass beingground and polished;

Fig, 2 is an enlarged sectional detail View of the lower surface of thegaging head oftheinspection apparatus, the glass and the glasssupporting table;

Fig; 3 is a vertical detail sectionthrough the easing head;

Fig. 4 is a top view oi the gaging head with the cover removed;

Fig. 5 is a horizontal sectional view of the gagingv heediekenSubstantially .on v4line -5-1-5 Aof Fig..v3;

Fig` 6 is a `front elevationv ofva -recordingand indicating device whichmay be use dwith the gag'ing head;

Figf7 is a diagrammatic vieu/ofA an'electrical system inV which thegaging head is the monitoringV element;

Fig.r8 is va cross-sectional, view ofa checking plete i011 the easinghead;.-

Fig. l.9 visa fragmentaryy sideqelevational view oa conventionaldouble-grinding system-wherein, a modied form `ofinspection apparatus isarranged; and o Fig. 10 isan enlarged cross-sectional detail view `ofthe modified for-m `of apparatus.y

Briefly stated, this invention is concernedwith the provision of amagnetic thicknessgagingin- .Simmern whichA is Sustained atapredetermined height above the surface ofthe glass sheetor othermaterial Ito be gageol.v Inthe development of the vinvention itwastoundthat-i a magnetic instrument were to be carried by asuitable-suppgfllgas @Montagen .the @ase could .be-supported upon a filmof uid, such as water, and maintained at a denite height by appropriatelimitation of the fluid pressure. Since the water or other fluid nlm issubstantially constant, the' container will be elevated or loweredrelativev to a known height or plane according to variations inthethickness of the glass, or other material, while at the same time nofriction will be created and no vibration above a minimum transmitted tothe container and the magnetic instrument therein Now, if the thicknessof the water nlm islestablished as well as the thickness of the layer ofthe embedding plaster for the glass sheet, their surnrnation,V when gtaken from the actual distance-between the lower surface o thesupporting case andfthe upper surface or top of the work table, willdetermine the thickness or" the glass By creating a magnetic eld ofcalculated strength between the magnetic instrument and the work table,any diierential of thickness will vary o the vv reluctance .of theymagnetic force ylines and consequently .producea reaction, which isrecorded.. in an electrical system or" which the magnetic instrument isa monitoring part.v

Referring now to the drawings and particularly to Fig. 1, there isdisclosed a portion of the well known continuous 4system for grindingandpolishingl plate glassandy including a series of work tablesA lc havingsecured upon the top thereof glass sheets Il by4 means of a layer ofplaster of Paris or the like indicated at l2. The glass sheets ll areembeddedin the layer of plaster in one area, or laying yard of thecontinuous grinding and polishingV system and are thence carriedrstbeneath grindingV lheads and, subsequently, beneath polishing runnersuntil the upper surface thereof is finished and the sheets are removedat the. completion oi the operation in the stripping yardl During thiscontinual processi there hask previously` been` no entirely satisfactorymethod devised wherein the thickness of the glass could be instantly,-or preferably continuously, checked. Asillustrated in Fig. l, noworking toolshave been shown since it will be made `quite apparent thatthe inspection apparatus herein provided can be located with equaladvantage between the individual grinding and/or polishing tools kor atvarious other points of the operation.

The inspection apparatus of this invention comprisesa gaging head,generally indicated by the numeral i3 in Fig. l, and a suitableindicating device indicated at lz The gaging head i3 isattach'ed by ailexible cable I5 to a framework It that issupported by standards l'ifrom the floor and bridges the work tablesY iii.v The connection of thecable -l5- is such'that it merely restrains the headV I3 fromy travelingwith the glass but otherwise imposes no restriction upon .freedom ofmovement of said head either in a vertical direction or laterally withrespect to the glass surface. Two exible conduits extend from the gaginghead i3; one, lsuch asthe conduit i8, carries the service lines from thesource of electrical energy and to thev indicating device Hl while thesecond is employed Vas aA water supply conduit i9. According to theinvention, the gacing head I3 is supported on a nlm of fluid, such aswater, or like mediums, supplied by the v*conduit I9, on-the-surface ofthe glass sheets ll and literally floats thereon, rising and fallingwith .any Variation of glass thickness as freely permitted by theexibility of the cable l5. Dui'- ing movementof therglass .progressivelybeneath the head i3, ,variations Iare. reproduced and amplied throughthe medium of the service conduit I8 and within the indicating device I4as will be more fully hereinafter described.

The gaging head i3 embodies generally a magnetic instrumentality ordevice A housed in a supporting case B. The case B comprises a tubularbody which is closed at the bottom by a plate 2l that is welded orotherwise sealingly secured to the lower peripheral edge of the tubularbody in a water-tight manner. The plate 2l is substantially larger indiameter than the body 2l) in order that the lower annular edge thereofmay be beveled or suitably rounded, as at 22, so that the plate willride freely over minor obstructions which are encountered particularlywhen the following edge of one sheet and the leading edge of a secondsheet pass beneath the head I3. Preferably the plate is of anon-magnetic or electrical conducting metal such as stainless steel orbrass.

At a point substantially below the upper rim of the body 2li, a shoulder23 is formed on the inner wall of the said body by reducing thethickness of the wall 24. Slightly above the shoulder 23, an annulargroove is provided in the upper, thinner section of the wall 24. Acircular plate 26 is arranged and supported on the shoulder 23 and toseal the lower area, or chamber 21 of the head I3 from moisture, agasket 28 may be placed on the shoulder before the plate 26 is locatedthereon. The plate is fixedly secured in its supported position by meansof an annular expansion ring 29 located in the groove 25. This ring is aconventional type of locking device which has an open section defined bytwo ends or spaced heads 3f! in which are located openings 3l by whichthe heads 30 may be urged toward each other by a suitable tool and thering compressed suiciently for its retraction from the groove 25. Uponrelease of the heads 30, the characteristic expansion of the ringspreads the same to its natural circular form and retains it in thegroove 25 provided for its function of locking. The body 20 is closed bya cover or lid 32 that is secured on the upper edge of the body by meansof suitable screws 33 or the like.

The plate 2B, on the shoulder 23, serves as the base for supporting themagnetic device A and also a terminal plate 3e by which one end of theflexible conduit I8 is connected to said device.

More particularly, the magnetic device A includes a transformer 35 whichis suspended from the plate 25 in such a manner as to permit itsvertical adjustment within the tubular body 2Q and escecially withreference to the bottoni plate 2 I. For this purpose, the transformer isprovided with a substantially H-shaped, laminated core 36 that isadapted to be carried in a generally vertical position by one, or themovable member 31 of a dovetail construction 38. The opposite orstationary member 35 of the dovetail construction 38 is secured byscrews d@ to the under surface of the plate 26 and serves to guide themember 3? in vertically directed movements. The member 31 is caused toslide with reference to Irhe dovetail surfaces dI (Fig. 5) of thestationary member 39 by means of a threaded shaft which is supported bythe threads thereof in a tapped opening 43 in the plate 25. The lowerportion of the shaft 42 is received in a bore de in the member 31 andadjacent the lower end thereof is provided with an annular groove L15 inwhich a pin tt is tangentially arranged, rihe ends of the pin 45 arecarried in a transverse bore 131 formed in the member 31 to position thecentral portion thereof within the groove to retain the shaft 42 fromendwise movement while permitting free rotation of the same.

The shaft 42 is provided with a driving slot 48 in its upper end and alock nut 49 is threadedly located on the shaft to secure the same in anyadjusted position to which it may be turned. The shaft is threaded inthe same manner as the shaft of the conventional micrometer; that is tosay, having forty threads per inch. By selecting this number of threads,one complete revolution of the shaft will obtain a rise or descent ofthe magnetic device A equal to twenty-five thousandths of an inch. Thelower ends 50 of the laminated core 3S may thus be located at anysuitable, approximated elevation above the upper surface of the plate 2I, or, when the gaging head I3 is operatively located on the surface ofthe glass, from the top 5i of the work table I0.

The gaging head I3, as previously set forth, is carried on the surfaceof the glass sheet II by means of a lluid film, such as water, and assupplied through the flexible conduit I9. For this purpose, the bottomplate 2l is provided with a relatively small, centrally disposed orice52. The orifice in the plate communicates with the conduit I9, connectedexternally of the head, through a pipe 53 that is secured at one end tothe plate, as by welding, in enclosing relation to the upper end of saidorifice. Preferably, the pipe 53 is suitably bent to extend across thesurface of the plate and rise along the wall of the tubular body 20 to apoint at which it passes through said wall and is connected at its outerend to the conduit. The huid under pressure may thus be conveyed from asuitable metering and/or regulating valve through the conduit I9 andpipe 53 to the orin'ce 52 in the plate 2| and flow therefrom at apressure which will create a nlm having sufficient pressure to supportthe gaging head I3 on and above the surface of the glass sheet I I.Since the pressure of the water may be maintained within suitablelimits, the lm of fluid created thereby will not vary despite thevertical movement of the gaging head in response to changing thicknessof the glass.

In connection with the above described water film, it is to be notedthat its constant formation creates a resultant emanation or escape ofthe water from beneath the gaging head I3. This acts to produceripple-like movements or a continual series of circula-rly and outwardlyexpanding waves. These waves, particularly across the leading area ofthe plate 2| of the gaging head, produce a consequent flushing actionwhich dispels any particles of glass or grinding abrasive from thesurface of the glass approaching the head. Introduction of foreignparticles into the supporting water film is thus prevented and obviouslythe gaging head will not be inadvertently raised from its establishedposition with reference to the surface of the glass.

The laminated core 36, carried by the slidably mounted member 31, ispreferably of an H- shaped formation. One vertically disposed leg 54 isxedly secured to the member 31 while the opposed vertical leg 55 carriesthe coils 5t and 51, one above and one below the horizontal web 58. Athird coil 59 is mounted on the web The coils 56 and 51 may be describedas "search coils, while the coil 59 acts as t' e power or exciter coil.The coils may be connected in a suitable electronic circuit, which willrespond to fluctuations in and between the coils 5S and 51 7 toproducathe.-actuationrof anindicating device, such as is shownin Fig.:6,and previously designated by the numeral I4.

This device is contained within a suitable case or cabinet 6I! and hasarrangedin the face there-A ofa dial I and pointer 62. According to thisinvention, the dial 6I is divided into fty increments of measurement 63and 6d on either side of a zero point indicated at 55 and the pointer62, when moved in a clockwise or counter-clock wise manner, serves todenote any increase or decrease from thezero point or a given standardas indicated by thepositioning of the pointer at this midpoint of thedial. Thus, for the purpose intended, the Zero point.65 may be assumedto be theaverage or standard thickness of a sheet of glass andmovementof the pointer therefrom in either direction assumed or taken asa decreased thickness or an increased thickness, When. the pointer 52rotates clockwise, the thickness of a sheet in one area may thus beincreasing above the standard and, when it rotates in acounter-clockwise direction, the sheet is diminishing in thickness andrunning below the standard. For example, during nnishing of the firstsurface of a glass sheet intended for what may be classified asone-.quarter inch plate, the average standard at one point of theoperation might be set at two hundred and ninety thousandths of an inch,whereas during the nishing of the second surface, the standard might betwo hundred and fifty thousandths of an inch.

Referring now to the enlarged sectional view in Fig. 2, the relativethicknesses of the plaster layer, the glass sheet and water film areindicated between the top 5I of the work table it and the under surface65 of the plate 2i of the gaging head I3. Now, it has been establishedthat the plaster of Paris layer i2 averages approximately seven.thousandths of an inch while the film of water, indicated at 51,maintains, at pressures between 10 and 30 pounds, a thickness ofsubstantially iive thousandths. This pressure is supplied through theorifice 52 in the plate 2i by the pipe 53 and conduit I9. It is to benoted that the thicknesses herein stated are not to be taken as absolutebut to be accepted as reasonably accurate calculations made undercertain operating conditions and within tolerances of from two to fourthousandths of an inch variance.

The coils 56, 51 and 59 ofthe magnetic device or transformer 35 areconnected by wires, grouped within the conduit I8, with an electricalsystem contained within the indicating device i5. More particularly,these connections are made in a manner which protects the moisture-tightcondition of the chamber 21 of the gaging head I3. The terminal plate 34thus carries a plurality of L-shaped conductor bars 68 on its uppersurface. The conductor bars have binding posts 59 at one endV thereof,'said posts `being anchored in the plate 34 and extending downwardlyfrom its under surface. The conductor bars 68 are provided with screws1! for securing wire connections from the conduit I8 above the plate 3dwhile nuts 1I are threaded onto the lower ends of the binding posts 65to secure the ends of connections from the transformer. Thus a wireI2-from 'one' side: ofthe coil 55 is connected through the r'st bar 68;Vthe joint wire 'i3 from the opposite side ofthe coil 55 and one side ofthe coil 51 `through the second barl 68, the i 14 from the oppositesideofr the coil 51 through the third bar-58 and the wires 15 and 15from 5 theV coil 59 through the fourth and fifth bars-,5,8 respectively.

The coil 59 is arranged between thecoils 55 and 51 to create a flow ofelectrical energy in approximately balanced relation circuitously.through each of said coils and the legs 54 and 55. of the core 35. Toproduce a completed, balanced magnetic eld through the coil 55, a re-Verence plate 11 is secured at one end to the sliding member 31 of thedovetailed construction 38 in spaced relation to the upper ends 123 ofthe core, and the distance between these ends it and` the plate 11 ismaintained despite the distance, set as a working standard between thelower ends 5@ of the core 36 andthe top 5I of the tables Ii). 'The spacebetween the ends 5d and the deci; thus determines the strength of thecompleted magnetic eld through the coils 51 and 59, the core 36 and thetable top. Y This space includes the thicknesses of the water film andlayer of plaster, which, as above stated, may be reasonably computedwithin close tolerances, leaving the thickness of the glass sheet as theonly varie able dimension and the one that can increase or decrease thespace established between theends 55 of the core 35 and the topr5! ofthework table Ill.

Generally stated the electrical system of this invention embodies abridge circuit wherein` the coils 55 and 51 are jointly connected to oneof the input of an amplier. Since the difierence between the magneticfields of the coils 55 and 51 will be reiiected in the conditions withinsaid bridge circuit and the operation of the amplifier, and furthersince the fundamental reason for this difference (the distance betweenthe coil 51 and the top 5I of the work table)v can-. not be entirelydissipated, a variable resistance is connected in series with this coilso ,that a bal,-l ance within the bridge circuit can be approached whenthe strength of the variable resistance is modified until the circuitthrough the ampliiier will produce a balance within the bridge circuit.For this purpose, the amplifying device causes the operation of acompensating motor which operatively alters the strength of the variablesistance connected in series with the coil 51. The coils arefundamentally arranged so that the magnetic field of one (coil 55)passes through the substantially fixed referenceplate 'i1 Vwhile fieldof the other (coil 51) is inuenced hy space existing between therespective coil 5i' and the top of the work tables, When a computedbalance has been established in the bridge cuit of these coils, anyvariation of glass thickness alters the physical distance between thecoil 51 and table top 5I and produces a consequent diiferential ofbalance in the input side of the amplier which is reflected throughoutthe system and sets the same into operation until a balance in thebridge circuit can be reestablished. This correction is mechanicallyinterpreted by means of the dial 6I and pointer 52 so that the extent ofunbalance created by the coils 51 can be translated into an exactmeasurement of the change in glass thickness.

The system also includes means whereby the bridge circuit can bebalanced according to initial existent conditions in order that thepointer 62 will be accurately positioned with reference to the zeroindication G5 on the dial 5 I. Further means are included to increase ordecrease the current iiow in that side ofthe bridge circuit, whichincludes the coil 51 and the variable resistance, to compensate forinequalities therein 9 so that the reading on the dial will besubstantially equal to and denote the change in the thickness of theglass sheet.

Referring now more specifically to the operation of the coils 56 and 51,there is disclosed in Fig. '1 an electrical system, in which the gaginghead I3 is the monitoring part, is illustrated as being representativeof electrical systems which may be used therewith. As herein provided, asource of electrical energy is supplied to the primary 19 of anisolating transformer 19 through line 80 from the side 8| of anelectrical source of supply and line 82 to the side 83 of the saidelectrical source. The secondary 84 of the transformer 19 is connectedby the lines 85 and te to opposite, xed contacts 81 and 88 of a controlswitch 89 having movable contacts 90 and 9|. Upon closure of thecontacts 81 and 99, a circuit through the line 92 is completed to oneside of the primary 93 of a reducing or step-down transformer 94 and bya branch line 95 to the supply side of an amplifier 96. Simultaneously,the contacts 88 and 9| complete a return to the line 86 from the primary93 by line 91 and a return branch line 98 from the supply side of theamplifier. Preferably fuses 99 are located in the lines 92 and 91 asshown.

The secondary of the reducing transformer 94 is connected by the lines15 and 16 .to the primary, or coil 59 of the transformer 35. The coils56 and 51 thus constitute the secondary of said transformer and theirrelated responsiveness to one another influences the circuit conditionswithin the input side of the amplifier 96. The wire 13 is connected incommon to each of Said coils 56 and 51 and completes the circuit to oneinput side of the amplifier.

The opposite side of coil 56, forming one side of the bridge circuit, isconnected by line 12 through limiting resistance |0| to the fixedcontact |02 of a variable resistance |03 and from the adjusting arm |04of said resistance by line |05, including a limiting resistance |06, toone side of a variable resistance |01, as at |08. The adjusting arm |09of the variable resistance |01 completes the circuit from the coil 56 tothe amplier 96 by line I|0. If desired, to stabilize the current flowand minimize noise and surges of undesired frequency, a condenser IIImay be located in bridge line ||2 between the lines |05 and ||0 and acondenser ||3 may be similarly interposed between the lines 13 and I|0,in branch line H4.

The line 14 from the opposite side of the coil 51 is connected to thexed contact ||5 of the variable resistance |01, the circuit includingcurrent limiting resistances I|6 in line 14 to the contact of theresistance and condenser I|1 in line ||8 from the fixed contact ||5 ofthe resistance |01 to line ||0.

A balanced condition can thus be obtained in the bridge circuit of thecoils 56 and 51 according to the magnitude of the resistance |01 sincethe side of said circuit through lines 14 and I|0 from the coil 51 tothe amplifier 96 may be thereby made to balance with the side of saidcircuit through lines 12 and |05 from the coil 56 by means of a motor II9 which is operatively associated with the adjusting arm |09 ofresistance |01. The main eld Winding |20 of this motor is connected tothe main lines 92 and 91 by lines I2| and |22 while the circuit of thesecondary or balancing winding |23 of said motor is completed by thelines |24 and |25 to the output side Yofv the amplier 96. The shaft |26of the motor ||9 carries the adjusting arm |09 of the resistance |01 andwhen conditions within the system vary the balance between the windings|20 and |23, the motor will be activated to rotate the arm |09 until theunbalanced condition existent in the bridge circuit of the coil 56 andthe coil 51 is corrected by adjustment of the variable resistance |01.

The magnetic field of the coil 56 is substantially constant beingthrough the coils 56 and 59, the core 36 and reference plate 11;however, as previously set forth, the magnetic eld of the coil 51 isdetermined by the distance existent between the top 5| of the work tableI0 and the core 36. Thus, any change in glass thickness will beindicated by a variance in the length of magnetic path of the field ofthe coil 51 and a consequent unbalance between the windings |20 and |23of the motor ||9 as reflected by the amplifier 96. This variance willcause the motor I9 to operate and, by the Shaft |26 thereof, swing theadjusting arm |09 until the potential through line ||0 and theresistance |01 equalizes the extent of unbalance existing between thesides of the bridge circuit and as determined by the coil 56 and thecoil 51 through line 13. To visually observe the amplitude of unbalance,the pointer 62 is also carried by the shaft |26 in order that the extentof this unbalance in the system may be computed and translatedmathematically so that the reading on the dial 6I will actuallyrepresent, in thousandths of an inch, the increase or decrease of glassthickness from the established standard of thickness.

The i ariable resistance |63 in the circuit of the coil 36 and betweenthe lines 12 and |05 thereof is employed to remedy initialout-of-balance conditions in said bridge circuit which are indicatedvisually on the dial 0|. One example of its use occurs when theinspection apparatus is placed in operation and the magnetic device A isprimarily positioned within the gaging head I9 according to thethickness of glass to be checked. When this thickness is an approximatedstandard for one-eighth inch glass, the ends 50 of the core 36 will bedisposed in closer relation to bottom plate 2| than for one-quarter inchglass. Likewise when three-eighths glass is to be inspected, the corewill be moved further from the plate'than for one-quarter inch glass.Obviously, the dimentional diierences herein stated are in the order ofone hundred and twenty-five thousandths and will greatly eXceed therange of the numbered scales on the dial 6 I. Accordingly, the threadedshaft 42 is now turned to raise or lower the transformer 35 until it issuitably located to operate within a small diierential of measurement ofthe estimated standard of thickness.

Preferably, the gaging head I3 is now placed upon a glass plate of thedesired thickness which is carried on a metal base, and a water filmcreated beneath the lower surface of the head. When the switch 8S isclosed, the coils 56, 51 and 58 will become activated and since thedistance between the upper ends 18 of the core 38 with respect to thereference plate 11 is maintained despite movement or adjustment of thelower ends 58 to an estimated distance from the table top 5|, an initialunbalance in the bridge circuit will be created between the coils 56 and51 and denoted on the dial 6| by reason of the fact that while thegaging head i3 is on a glass plate of standard thickness, the magneticfield of the coil 51 will be through said coil, the coil 59, the core 36and the metal base of the standard plate.

ends 5t' of the transformer 35. This produces a variation in the balanceeffected in the bridge circuit between the coils 5t and El', the ield ofcoil 5S being substantially constant between the upper ends 'iS of thetransformer and the refere ence plate l1. Now this change or decreasingof the neld of the coil 51 will be transmitted by the line 16, throughany currently adjusted setting of the variable resistance |01, to theline I and one input side of the amplifier S5. Since the common line 13of the coils is connected to the opposite input side of said amplifier,the lines |24 and 25 from the output side thereof will change thecharacter of the current through the secondary winding |23 of the motorl and consequently produce a differential between the Winding B23 andthe main winding iZEl which is connected by lines |21 and [2 to the mainelectrical supply lines S2 and 91.

The motor It will thus be caused to rotate the shaft it in a clockwisedirection so as to bring the potential through the adjusting arm it ofthe variable resistance |131 and line I it equal to the potential ofline 'i3 to the input sides of the amplifier Q5, thereby balancing thebridge circuit of lines 1J!- and i2 and it to line i Simultaneously theshaft |25 will carry the pointer d2 in a clockwise direction withreference to the measured increments of the dial 5|. Since the spacingbetween these increments is calibrated to linearly express the extent ofcorrection required in the electrical system, the physical means forlengthening the path of the magnetic field of the coil 51 or, morespecifically, the increased thickness of the glass sheet, will bedirectly readable by the position of the pointer S2 in relation to theincrements on the dial. For example, if the standard thickness for theirst surfacing of a glass sheet should be set at two hundred and nintythousandths of an inch, where the thickness in one area approaches threehundred thousandths of an inch, this increase will produce the resultantelectrical reaction within the system to activate the motor ||9 untilthe arm |09 of the variable resistance ||i1 makes the necessarycorrection and by so doing similarly carries the pointer B2 intoregistration with the legend Ib in the increments of measurementConversely, where the grinders are removing too much glass from thesurface of the sheet, the transformer 35 of a gaging head i3 in thisarea will create a chain of functions which will cause the pointer 62 toswing counter-clockwise until the extent of glass removal, below thestandard required, is denoted by the pointers position in relation tothe increments t3 on the dial. Since even the diierence of surfacelevels occurring between the adjoining ends of two sheets will beinstantly denoted by rapid rotation of the pointer in one direction orthe other, a continual record graph can be studied and the thickness ofany particular sheet readily determined.

Now, if the thickness of glass is reduced, as for example, from astandard of two hun-dred and ninety thousandths of an inch, for the rstsurn face of one-quarter inch glass plate to one hundred and seventythousandths of an inch for the first surface of one-eighth inch glassplate, the indicating device will not be able to adequately functionsince the difference is too great for the permitted range 0f theinstrument. According ly, the gaging head i3 is removed from itscperating area and the cover 32 is removed therefrom. The nut 49 on theshaft 42 is loosened and said shaft is turned to lower the transformerv14 35 until the lower ends 50 thereof are suitably spaced inapproximate distance from the top of the work table. This, of course, isdetermined by placing the gaging head on the desired checking plate |3|and observing the position of the pointer 62 relative to the dial 6|.

However, since the difference is in the order of one hundred and somethousands of an inch between the standard thicknesses, advantage may betaken of the thread formed on the shaft 42 which, as previously setforth, may be the conventional micrometer screw of forty threads perinch. By so turning the shaft as to produce substantially five completerevolutions thereof, this major difference can be readily relieved andthe transformer 35 moved to a lowered position so that when the gaginghead is placed upon the checking plate, the indicated difference on thedial 6| may only be a few thousands of an inch out,v either way, fromthe zero indication which denotes the standard thickness required.

It is now possible by means of the knob |21 on the cabinet 60 to adjustthe setting or position of the pointer 62 in relation to the Zeroindication 65. By turning the knob |21, the arm |04 of the variableresistance |03 may be shifted until the consequent change in currentoutput from the amplifier 96 causes the motor ||9 to sufficiently changethe current flow through the variable resistance |01 and the sides ofsaid circuit through coils 56 and 51 to shift the pointer to the midwayposition on the dial. The lock nut 49 on the shaft is then returned tosecure the shaft 42 and the cover 32 of the gaging head properlyreplaced.

The head |3 is now corrected for indicating the various thicknesses of athinner sheet of glass with the possible exception that in producing abalance in the bridge circuit between the coils 55 and 51, thecorrection may have produced a change in the magnitude of currentthrough the variable resistance |01. As previously pointed out, thiscondition reduces or increases the extent of movement of the pointer 62,visually, so that the measurement of its movement is not equal to agiven increase or decrease of glass thickness. to the adjusting arm |34of the variable resis tance |32 in parallel with the resistance |01, maynow be manipulated to compensate for the differential of voltage so thatthe variance of glass thickness can be accurately computed. Thismodication can also be made while the head I3 is on a checking plate |3|since the amount of difference between the plates |28, |29 and |30thereon has been previously established.

According to this invention, as above set forth, it is now possible tocheck the thickness of moY ing sheet material, having non-magneticcharacteristics, and to obtain such measurements as may be desired incritical areas heretofore considered impossible, or at least,impractical to reach. While the description of this inspection apparatushas, by way of example, been directed to one application or" itsadvantageous use, it is to be pointed out that there is no stringentrequirement that the same is useable only in connection with glass orthat the supporting nlm should or must be of a liquid character. Thus,without any appreciable alteration of the apparatus, the gaging head |3can be employed to inspect the thickness of materials which at one pointor another in their processing are maintained at temperatures well abovethe boiling point of water; or like liquids which may be sub- The knob|38, operatively connected rollers.

. epesses Y is stituted therefor in accordancef'with. .alliedI-steps ofaA particular process. LASuitable::gaseous Zele* -ments maybeequally1used to good-i advantage method `of operation'-for-:producingplatelgl'ass,

the ribbon of glass, indicated bythewnumeral M3,- rnovesdirectly fromthe `usual*4 annealing lehrf toward and-between the i-verticallyeoppcsedgrinding tools 4M. 'i These-1toclst `are equipped.'v .to

grind the glass-surfaceswinaemannersimilarte l that followedrinsingle-surfacing; 1 .This `method isknown as double ortwin lgrinding uand. `no support is afforded Vfor the/continuous ribbonJ 4-of glassother than the grinding tools.A or` interpcsed That is tof-say; asfpreviousl'yf described, l. 'the glass wasconsideredirrthe light V of:individual lsheets and' these" sheets were-carriedon frnetallic Vtablesin abed-fof plaster oiParis'zori -theilika but Vwhen both` surfaces arefbeing, actedwupony-no comparable support isaifoi'deduforfvthe continu-Iwork table IG. I'Thus aeplateffl' :of magnetic :material isdisposedagainst' thevundersurface of theglass-ribbon'andisspacedfthereroni byAthe--samevmeans asA that employed tohsupport the -gaging head 4I31onthe upper surface.

bodied in anannular,E flat f contacting -v member "LMS having atubularstem-'Mldependingtherefrom; "The stem.- I'AI islpref'erablylprovidedWith ashoulder IAS: midwayiof' its length 'Wh-ich shoul- 'derisf'receivedby athrustbearingill'- carried in a collar i |155.' -:The7collar .|250` is lexinglyf Ysupported-l by means of afparallelograrnframe- I 5 I-.so

.that the 1member`A M52 is vinstantaneously--remov- Iable from thevicinity'of .the glass surfacezthough it is'normallyurgedthereagainst;

The periphery ofi the contactinginember:y I 4B is suitably rounded; aasat'l52-sonthat surface will vnot abruptly Istrike Athe same`Yand,'1should the ribbon shatter,v the' on-,comingedge willsucientlydeflect the member -until it can rdeithereunder and returntd-its normalspacedgposition. The contacting rnernber |46 is held,` inspacedrelation, at aY predetermined distance, bymeans ,of a lm of-fluidwhichis released inthe central Vareav of the rnernber` at av suitablylimited?. pressure of sucientforce to'createaconstantlyfde- `nnablespace.` Thisfluid, whichinthe-instance of glass; may -beA water, is'conveyed byisuitable piping to the end-ofthe tubular stem-IM.' VForthis purpose-the. stem is tapped to receive a com `ventional swivelpipeconnection .I53 and the tubular chamber i 'I 541 terminates 1 inaysmall; orif nce I 55 formed centrally in, thecontacting-member-M6.

.. :The parallelograrn ,frame Il; ismountedmy a suitable.- bracket-.rl5seen: thettlcorr; oreadjoining defects or Otherirregularitiesiof themovingfglass framework of 'the grinding equipment. The f'rarne comprisespairs of legs 157, which `e -repiv otally supported at one end by shafts.i158 Olathe bracket 156; At their upper ends, the pairs of legs 'lcarrythe'collar itt?V by means ofstuds I5 secured in bosses lee integrallyformedn the periphery of vthe collar. T helegs Ij5l are caused to swingin an upward direction byrneans of a coil spring It! which is anchoredat one end Atothe bracket les and attached at its 0ppcsite end to one ofthe legs l5? by a. bolt `|62. By this arrangement, the legs 51, inunison, urge the collar upwardly and thereby direct the upper surfaceit@ of the member Ill@ against-the undersurface of the glass ribbon It.However, when this spring pressure is urging the reference plate i155against-the glass, asupply ofgiluid, such as. water at a suitablylimited pressure, v is directed through the orice 155 to establishliquid :film-therebetween. The pressureeiiected by the springv it! willthus, be somewhat equalizedby the existence of the liquid ln'iand theextent of equalization is determined by the desired thicknesscf iilm tobe maintained,

l?relin'iinaryl to using the inspection apparatus in connection with adouble grinding system, the gaging head I3 and rthe plate'li arearranged at substantially the saine elevation as thatfgin which theglass ribbon passes through-theygrinding-tools. By introducing a glassplate of standard thickness between the head i3 and` the-plate -lfieandcreating their respective liquid-films,l the indicating device is can beadjusted, aspreviously described. The position of the parallelogramframe may now be ascertained by suitable means so that when positionedinthe line ofthe movingglass, the frame will support theplate ist at thesame spacial distance from the-gaging head. This can, of course, beperformed in other ways, the essential factor to-be determined beingthat some arbitrary spacing is obtained which may be considered as thestandard` distance between the head and the plate. A

-In use, the gaging head I3 is placed Yupon Vthe upper Vsurface ofthe'glass ribbon |43 and a film of water, such as previouslyindicated-att? in Fig. 2, and also in Fig. l0, iscreatedbeneaththe'undersurface 5S of the plate 2i. The plate 145 isfnow positionedagainst the under surface of the glass and a iilrn of water, asindicated-at ISG, in Fig. l0, is created beneath said surface of theglass and the surface |53 of the plate. since the thickness of each ofthese films (t1 and ist) may be estimated within close dimengrindingtools I idgthe variations of thicknesgwill `produce variations withinthe electrical system,

which variations will be indicated on the dialll by means of the pointer62.

It isto be understoodthat the form of the invention herewith shownand'described is to be tagenas a preferred embodiment of the same, butthat various ,changes in the shape, size and arrangement ofgparts may beresorted to Without departing. from the spirit of theinvention orthe-scope of the subjoined claims.

.Weclairnz l'irAnfapparatusfor determiningthe thickness of anon-magnetic material from one surface thereof, comprising a magneticsurface beneath the non-magnetic material, means including a supportingcase positioned above said surface, means supplying a film of fluidbeneath the supporting case to maintain the same at a predetermineddistance above the non-magnetic material, a normally balanced electricalsystem, means constituting a part of the electrical system mountedwithin said supporting case for creating a magnetic neld which varieswith changes in the distance between said case and said magnetic surfaceto create an unbalance in the electrical system, means for indicatingthe changes in the distance between the case and the magnetic surface,and means operable Within the electrical system to balance currentconditions when a change in said distance occurs.

2. An apparatus for determining the thickness of a non-magnetic materialfrom one surface thereof, comprising a magnetic surface beneath thenon-magnetic material, means including a supporting case positionedabove said surface, means supplying a nlm of fluid beneath thesupporting case to maintain the same at a predetermined distance abovethe non-magnetic material, a normally balanced electrical system mountedwithin said supporting case for creating a magnetic field which varieswith changes in the distance between said case and said magnetic surfaceto create an unbalance in the electrical system, means for indicatingchanges in the distance between the case and the magnetic surface, andmeans operable within the electrical system to balance currentconditions when a change in said distance occurs.

3. An apparatus for determining the thickness of a glass sheet mountedupon a metallic supporting surface and moving in a substantiallyhorizontal path of travel, comprising a gaging head including asupporting case positioned above said supporting surface, meanssupplying a film of fluid beneath the supporting case to maintain thesame at a predetermined height above the glass sheet, an electricalindicating system, means mounted Within the gaging head and constitutinga part of the electrical indicating system for creating a constantmagnetic field and a variable magnetic field, the magnitude of variablemagnetic field being determined by the elevation of the gaging headabove the supporting surface whereby an unbalance between the saidmagnetic fields will cause a response within the indicating system todenote an increase or decrease of glass thickness from a given standard,and means operable within the electrical indicating system to balancecurrent conditions when the glass thickness varies from the givenstandard,

4. An apparatus for determining the thickness of a sheet of glass fromone surface thereof, comprising a metallic surface above which saidsheet is supported and carried in a substantially horizontal path oftravel, a gaging head including a supporting case positioned above saidsurface, means supplying a lm of fluid beneath the supporting case tomaintain the same at a predetermined height above the surface of theglass, an electrical indicating system, magnetic means mounted withinthe supporting case and constituting a part of the electrical indicating`system for creating a variable magnetic field between the gaging headand the metallic surface and a constant magnetic eld, said variablemagnetic field being responsive to the changes in glass thickness andproducing an unbalance within the electrical system, means for obtaininga balance between the magnetic fields according to predeterminedstandards of glass thickness whereby the unbalance between the saidmagnetic fields may be computed as a variance in glass thickness fromthe predetermined standard, and means operable within the electricalindicating system to balance current conditions when the variance inglass thickness occurs.

5. An apparatus for determining the thickness of a sheet of glass fromone surface thereof, comprising a metallic table upon which said sheetis supported and carried in a substantially horizontal path of travel, agaging head including a supporting case positioned above said table,means supplying a nlm of fluid beneath the supporting case to maintainthe same at a predetermined height above the surface of the glass torise and fall therewith during changes in glass thickness, means forrestricting c iovement of the gaging head to vertical and horizontallylateral motions with reference to the surface of the glass, anelectrical indicating system, means mounted within the supporting caseand constituting a part of the electrical indicating system for creatinga variable magnetic field between the gaging head and the metallic tablein comparison to a constant magnetic eld, means for obtaining a balancebetween the variable and constant magnetic fields according topredetermined standards of glass thickness, means operable within theelectrical indicating system to balance current conditions when changesin glass thickness occur, and means for varying the mounted relation ofthe said magnetic means within said supporting case to compensate forchanges in the predetermined standards of glass thickness which exceedthe operating range of the electrical indicating system. i

6. An apparatus for determining the thickness of a glass sheet from onesurface thereof, comprising a magnetic surface above which said sheet iscarried in a substantially horizontal path of travel, a gaging headcomprising a supporting case having a non-magnetic bottom wall, meanssupplying a film of fluid beneath the supporting case to maintain thesame at a predetermined height above the surface of the glass sheet toraise and lower the same therewith during changes of glass thickness,means for restricting movement of the supporting case to vertical andhorizontally lateral motions with reference to the surface of the glass,an electrical indicating system, normally balanced magnetic meansmounted within said supporting case and constituting a part of theelectrical indicating system, said magnetic means including a constantmagnetic field and a variable magnetic eld, the magnitude of thevariable magnetic eld changing with the rise and fall of the gaging headto produce an unbalance between the magnetic fields and create aresponse within the electrical indicating system to visually denote suchchange of glass thickness, and means operable within the electricalindicating system to balance current conditions.

7. An apparatus for determining the thickness of a glass sheet from onesurface thereof, comprising a metallic table upon which said sheet issupported and carried in a substantially horizontal path of travel, agaging head comprising a supporting case including a closure cover atone end and a non-magnetic plate forming the bottom wall thereof, thebottom wall having an orifice of small diameter centrally formed there-1n, means supplying a fluid under limited pressure to said orifice andtherethrough for supporting the gaging head on a-lm of fluid at apredetermined height above the surface of the glass, a mounting platesupported above the bottom Wall of the supporting case, a stationarymember depending from said plate and having a Vdovetail groove formed inone face thereof, a slide member having engaging surfaces interttingWith the dovetail groove of the stationary member, an electricalindicating system, a transforme1' secured to said slide member andconstituting a part of the electrical indicating system, saidtransformer including a core, a primary coil, and ya divided secondarycoil, means obtaining a constant potential through one part of thedivided secondary coil and maintaining a magnetic eld of known capacity,the second part of the divided secondary coil being positioned to effecta magnetic neld of variable potential with the top of the metallictable, means operable within said electrical indicating system forbalancing current conditions therein according to the varied potentialof one side of said secondary coil and including means ior visuallyindicating a change from the predetermined height of the gaging headabove the top of the metallic table during correction of the balancewithin the electrical indicating system.

8. An apparatus for determining the thickness of a glass sheet from onesurface thereof, comprising a metallic table upon which said sheet issupported and carried in a substantially horizontal path of travel,argaging head comprising a supporting case including a closure coveratone end thereof and a non-magnetic plate forming the bottom Wall havingan oriiice of small diameter centrally formed therein, means supplying afluid under pressure to said orice and therethrough for producing a lmof fluid beneath the supporting case to support the same at apredetermined height above the surface of the glass sheet, a mountingplate supported above the bottom wall of the supporting case, astationary member depending from said mounting plate and having aVdovetail groove formed in one face thereof, a slide member havingcorrespondingly engaging surfaces intertting with the dovetail groove ofthe'stationary member, a shaft threadably supported in said mountingplate, one end of said shaft being rotatably received within the slidemember, means for securing the shaft from endwise movement relative tothe slide member while producing vertical movement of the slide memberwith reference tothe stationary member, an electrical indicating system,a transfOrmer constituting a part thereof, said transformer beingsecured to the slide member and including a core, a primary coil and adivided secondary coil, a bar secured to one end of the slide member inspaced relation to the transformer core and adapted to eii'ect amagnetic iield of substantially constant potential with one portion ofthe divided secondary thereof, the threaded shaft being rotatablerelative to the mounting plate to raise and lower the slide member andtransformer Carried thereby with reference to the bottom Wall of thesaid supporting case to obtain a preliminaryT spacing of saidtransformer from the top of the metallic table whereby a magnetic fieldfrom the second portion of the secondary can be completed with said topof the metallic table which varies with the distance between saidcasevandsaid metallic table to denote the thickness of glass passingtherebetween.

9. An apparatus for determining the thickness of acontinuous ribbon ofglass moving in a substantially horizontal path of travel, a gaging headcomprising a supporting case including a closure cover at one end and anon-magnetic plate forming the bottom wall thereof, the bottom wallhaving an oriice of small diameter centrally formed therein, meanssupplying a fluid under limited pressure to said orifice andtherethrough for supporting the gaging head on a nlm of fluid at apredetermined height above the surface oi the glass, a plate supportedabove ie bottom wall of the supporting case, a stationary memberYdepending from said plate and having a dovetail groove formed in oneface thereof, a slide member having engaging surfaces interntting withthe dovetail groove of the stationary member, an annular plate nexinglysupported beneath the glass ribbon and including a tubular dependingstem, the plate having an orifice of small diameterk centrally formedtherein, means supplying a iiuid under limited pressure to the tubularstem and outwardly through the orifice for sustaining said annular plateat a predetermined distance from the under surface of the glass ribbonand the gaging head, an electrical indieating system, a transformersecured to said slide member and constituting a part of the electricalindicating system, said transformer including a core, a primary coil,and a divided secondary coil, n sans obtaining a constant potentialthrough one part of the divided secondary and maintaining a magnetic eldof known capacity, the second part of the divided secondary coil beingpositioned to effect a magnetic field of variable potential With thesurface of the annular plate, means operable within said electricalindicating system for balancing current conditions therein according tothe varied potential of one side of said secondary coil and includingmeans for visually indicating a change from the predetermined distanceof the gaging head from the annular plate during correction of thebalance within the electrical indicating system, and adjusting means tomove the slide member with reference to the stationary member therebyadjusting the position of the transformer to compensate ior changes instandards of glass thickness beyond the operating range of theelectrical indicating system.

gaging head on a film of fluid at a predetermined` height above thesurface of the glass, an electrical indicating system, a transformercarried Within the supporting case and constituting aY part of theelectrical indicating system, said transformer including a core, aprimary coil, and a divided secondary coil, means obtaining a constantpotential through one part of the divided secondary coil and maintaininga mag'- netc field of known capacity, the second part of the dividedsecondary coil being positioned to effect a magnetic field of variablepotential with the top of the metallic table, and means' operable'Within said electrical indicating systemV 21' for balancing currentconditions therein according to the varied potential of one side of saidsecondary coil and including means for visually indicating a change fromthe predetermined height of the gaging head above the top of themetallic table during correction of the balance within the electricalindicating system.

l1. An apparatus for determining the thickness of a glass sheet from onesurface thereof, comprising a metallic table upon which said sheet issupported and carried in a substantially horizontal path of travel, agaging head including a supporting case having a closure cover` at oneend thereof and a non-magnetic plate forming the bottom wall having anorice of small diameter centrally formed therein, means supplying afluid under pressure to said orifice and therethrough for producing aiilm of fluid beneath the supporting case to support the same at apredetermined height above the surface of the glass sheet, an electricalindicating system, a transformer constituting a part thereof, saidtransformer carried within the supporting case and including a core, aprimary coil and a divided secondary coil, a bar mounted in spacedrelation to the transformer core and adapted to effect a magnetic fieldof substantially constant potential with one portion of the dividedsecondary thereof, and adjusting means to raise and lower thetransformer with reference to the bottom wall of the said supportingcase to obtain a prelinimary spacing of said transformer from the top ofthe metallic table whereby a magnetic field from the second portion ofthe secondary can be completed with said top of the metallic table whichvaries with the distance between said case and said metallic table todenote the thickness of glass passing therebetween.

12. An apparatus for determining the thickness of a continuous ribbon ofglass moving in a substantially horizontal path of travel, a gaging headincluding a supporting case having a closure cover at one end and anon-magnetic plate forming the bottom wall thereof, the bottom wallhaving an orifice of small diameter centrally L,

the glass, an annular plate iiexingly supported r beneath the glassribbon and including a tubular depending stem, the plate having anorifice of small diameter centrally formed therein, means supplying afluid under limited pressure to the tubular stem and outwardly throughthe orifice for sustaining said annular plate at a predetermineddistance from the under surface of the glass ribbon and the gaging head,an electrical indicating system, a transformer carried within thesupporting case and constituting a part of the electrical indicatingsystem, said transformer including a core, a primary coil, and a dividedsecondary coil, means obtaining a constant potential through one part ofthe divided secondary coil and maintaining a magnetic eld of knowncapacity, the second part of the divided secondary coil being positionedto effect a magnetic neld of variable potential with the surface of theannular plate, means operable within said electrical indicating systemfor balancing current conditions therein according to the variedpotential of one side of said secondary coil and including means forvisually indicating a change from the predetermined distance of thegaging head from the annular plate during correction of the balancewithin the electrical indicating system, and adjusting means to raise orlower the position of the transformer te compensate for changes instandards of glass thickness beyond the operating range of theelectrical indicating system.

13. An apparatus for determining the thickness of a non-magneticmaterial from one surface thereof, comprising a horizontally disposedmagnetic surface supporting the nonmagnetic material, means including asupporting case positioned above said surface, means supplying a lm offluid beneath the supporting case to maintain the same at apredetermined distance above the non-magnetic material, the bottom Wallof the supporting case being of a non-magnetic material, a verticalstationary guide member mounted Within said case, a slide member carriedby said stationary guide member and vertically adjustable thereon, anormally balanced electrical system, means constituting a part of theelectrical system mounted upon said slide member for creating a magneticfield which varies with changes in the distance between said case andsaid magnetic surface to create an unbalance in the electrical system,and means operable within the said electrical system for balancingcurrent conditions therein.

14. An apparatus for determining the thickness of a non-magneticmaterial from one surface thereof, comprising a horizontally disposedmagnetic surface supporting the non-magnetic material, means including asupporting case positioned above said surface, means supplying a film offluid beneath the supporting case to maintain the same at apredetermined distance above the non-magnetic material, the bottom wallYof the supporting case being of a non-magnetic material, a mountingplate supported above the bottom wall of said case, a stationary guidemember depending from said plate, a slide member adjustably carried bysaid stationary guide member, an electrical indicating system, meansconstituting a part of the electrical system mounted upon said slidemember for creating a constant magnetic eld and a variable magneticfield, means operable within the electrical indicating system tonormally balance the current conditions therein, the magnitude of thevariable magnetic field being determined by the elevation of thesupporting case above the magnetic surface whereby an unbalance betweenthe said magnetic fields will cause a response within the electricalsystem to denote an increase or decrease of thickness of thenon-magnetic material from a given standard.

15. An apparatus for determining the thickness of a glass sheet mountedupon a metallic supporting surface and moving in a substantiallyhorizontal path of travel, comprising a gaging head including asupporting case positioned above supporting surface, means supplying afilm of nuid beneath the supporting case to maintain the same at apredetermined distance above the glass sheet, the bottom wall of thesupporting case being of a non-magnetic material, a mounting platesupported above the bottom wall of said case, a stationary guide memberdepending from said plate, a slide member adjustably carried 'by saidstationary guide member, an electrical indicating system, meansconstituting a part of the electrical indicating system mounted upon theslide member for creating a constant magnetic field and a variablemagnetic eld, means operable within the saidelectrical. indicatingsystem to normally balance the current conditions therein at a givenstandard of .glass thickness, the magnitude of the variable magnetic eldbeing determined by the elevation of the gaging head above the metallicsupporting surface whereby ank unbalance between the said magneticeldswili cause a respense within the indicating system to denote anVincrease or decrease of glass thickness from the given standard.

DONALD W. DUNIPACE.

NORMAN C. NITSCHKE.

References Cited `in the file of this patent UNITED STATES PATENTSNumber Long Feb. 6, 1951

